The need for cooling, condensing, humidifying or stripping of dissolved or entrained gases from liquids is well known. The burgeoning need for cooling large volumes of water in electrical utility generating plants, industrial condensing or cooling systems, and commerical and industrial air conditioning systems also is well known. The expanding nuclear power industry in particular has been plagued currently with the problem of cooling large quantities of water in order to reduce the temperatures of the thermal discharge from generating stations for ecologically oriented reasons.
Cooling of water has been performed heretofore primarily by cooling towers and spray ponds.
Entrainment of droplets in the air traversing the spray is a problem common to both cooling towers and spray ponds. If the droplets are carried away from the cooling system, they are lost to the system and the cooling efficiency is reduced. In cooling towers drops of water are entrained in the forced draft of air. In spray ponds, a mist often is formed which can be carried away by the wind. If the water is brackish, injury to surrounding environment by water carried away by the air can produce adverse ecological disturbances. Salt water damage in areas surrounding cooling systems can be especially severe.
Very fine sized droplets can readily be entrained in moving air. In the cooling towers, the water splashes to different layers as it descends through the tower and produces droplets of various sizes, including the very fine droplets that are entrained in the draft of air through the tower. For this reason, cooling towers which employ brackish water present significant problems to the environment.
In addition to the problem of entrainment of fine water droplets, there are other difficulties in cooling towers. Cooling towers often require structures which are expensive to construct and in many cases unsightly in their appearance. Cooling towers are often plagued with an accumulation of algae so that they must be periodically cleaned. The efficiency of many cooling towers drops through the years. Ordinarily cooling towers perform at peak efficiency only when new, and the deterioration of materials allows the water to channel as a stream, and not as broken droplets, so that heat transfer efficiency drops sharply and plant operating expense increases sharply due to less effective cooling.
Spray ponds in which a number of nozzles spray water into contact with the surrounding air also are employed for cooling water. Spray ponds, however, are dependent upon wind for their highest cooling efficiency, and the construction of spray ponds necessarily have been designed to achieve the most effective use of prevailing winds in the pond area. If there is not adequate prevailing wind, or if such wind is unpredictable, the efficiency of the spray pond is similarly affected.
The efficiency of spray ponds illustrated in the foregoing patent depends to an important extent upon the wind velocity. Cooling by spraying is largely the result of some evaporation of water from the spray droplets, termed mass transfer. It will be realized, therefore, that cooling which is the sum of the mass and sensible heat transfer, is a function of the amount of air, and hence the velocity of air, traversing the water surface of the droplets during their trajectories through the atmosphere. The velocity of the air is dependent in turn ordinarily upon the natural conditions which produce wind.
The unpredictability of wind and its velocity presents a problem to cooling water by spraying. In some areas, many days have no wind, and the cooling efficiency by spraying is severly reduced.
For example, in the spray device illustrated in Ser. No. 273,181, filed July 19, 1972, now U.S. Pat. No. 3,771,724 the air traversing the spray is dependent substantially entirely upon natural conditions. At times when the wind velocity is high, the capacity of cooling by spraying in a given unit is high. If, on the other hand, the wind velocity is very low, or nil, cooling capacity can be severely reduced.
Spray devices also can be used advantageously, apart from cooling, to humidify air or to strip dissolved or entrained gas from water or liquids. In each of the foregoing uses, the velocity of the gases traversing the liquid spray is important to the capacity of the system.